Blender Game cell shading
The Scale operation works in relation to the object origin - so for a cube with the origin placed at the centre you get the desired effect - ie, you end up with a larger cube with faces parallel to the original and at a consistent distance. 

For more complicated models this same technique does not work as you have found. One solution (depending on your mesh) is to use a Solidify modifier with a negative Thickness. 



Another option (if the Solidify doesn't produce useful results) is to duplicate the original mesh and use a Shrinkwrap modifier on the duplicate, set with the original mesh as the Target. Set mode to Project and adjust the Offset for the thickness.